In most automobiles with a manual transmission, transmission rattle occurs. The noise arises when freely rotating gear teeth strike each other at a certain frequency when they are accelerated in the gearbox due to non-uniform running of the engine at low rpm. The oscillations occurring are promulgated via the clutch and the input shaft and are due not only to the engine but also to the drag force of the gearbox. The engine flywheel has a greater angular acceleration and oscillation amplitude at low rpm, so that the rattle increases in most cases as the engine speed is reduced.
Several different methods of reducing or completely eliminating rattle in gearboxes are known. It is possible for example to use clutches of special stiffness and damping, to increase the moment of inertia of the flywheel or to decrease the backlash between the gears. For considerations of function and production, it is not possible to reduce the backlash enough to achieve effective damping.
A number of the abovementioned disadvantages are eliminated by an arrangement in which one gear in a pair of interengaging gears has a hub portion on which a gear in the form of thin disc with the same gear-tooth shape and number of gears as the gear itself is rotatably mounted. Between the gear and the gear disc there is mounted a spring element which is biased towards the engaging position of the gears. Such an arrangement is inexpensive to manufacture, has high efficiency and makes it possible due to its damping to avoid the effect of the inherent frequency of the transmission components.
However, this arrangement has certain limitations: firstly, the backlash is only eliminated between those gear pairs which have a gear with a biased gear disc and, secondly, such a gear disc cannot for practical production reasons, be disposed on that side of a gear which has coupling teeth for engagement with an engaging sleeve, which to a certain extent can limit the freedom of design of a gearbox.